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Narrator:
Our solar system --
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8 planets and over 300 moons
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circling the Sun like clockwork.
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But it didn't start that way.
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Our solar system
has a long history of violence.
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The solar system we see today
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is really just the final
survivors of the early chaos.
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Narrator: And in the future,
that chaos will return.
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The entire house of cards
that is our solar system
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will completely fall apart.
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Narrator:
From start to finish,
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this is how solar systems work.
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There are billions of stars
in the Milky Way galaxy.
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One of them is our Sun.
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And around the Sun orbits
a system of planets and moons --
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a solar system.
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Our solar system is clearly
a precious planetary system.
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And it begs the question,
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are there other
planetary systems like ours
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orbiting other stars?
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Narrator: To find out, Marcy
scans the skies with the Keck --
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one of the world's largest
optical telescopes.
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Perched at 14,000 feet,
on top of Mauna Kea in Hawaii,
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it hunts for new,
distant solar systems.
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The marvelous reality is
that our own Milky Way galaxy
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contains some
200 billion stars or so,
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and many of those stars have
their own planetary systems.
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Our solar system,
with its eight major planets,
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is not alone.
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There are other
brethren planetary systems
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out there by the billions.
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Narrator: Of course, astronomers
hope to find another solar system
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with a planet like Earth,
and they're off to a good start.
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So far, Marcy
and other astronomers
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have discovered over 360 stars
with orbiting planets.
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Marcy: One of the exciting
discoveries that we've made
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is that stars
tend to be orbited
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not just by one planet
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but usually two, three, four,
or a multitude of planets.
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Planets come in families,
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not unlike the family of planets
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we enjoy here
around our own Sun.
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Narrator:
For the first time,
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scientists can study them
in some detail.
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We can actually observe
how planets heat up
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as they go around their sun.
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For example, we actually saw
that one planet
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got hotter and colder
as it orbited its star.
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And we realized
that we were actually seeing
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the night side of the planet
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and then the day side
of the planet.
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That was
the temperature difference.
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We were observing sunrise
and sunset on a planet
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in another solar system.
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Narrator: But that planet
is nothing like Earth,
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and most of these newly
discovered solar systems
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are nothing like our own.
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Their planets are huge --
much bigger than Jupiter.
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Some follow wild orbits,
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some orbit
in the opposite direction,
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and some shoot billions
of miles out into space,
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then dive back
toward their star.
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A few orbit so close
to the star,
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their surfaces vaporize.
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It's bizarre, at the least,
if not completely frightening.
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Planetary systems
offer a wide diversity
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of different architectures,
sizes,
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masses of the planets,
and so on,
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rendering our solar system
just one type
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of a planetary system
out of thousands.
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Narrator: It could be that each and
every solar system is a one-of-a-kind.
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But they all have one thing
in common --
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each one begins with a star.
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First, a star is born in a cloud
of dust and gas called a nebula.
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This is the Eagle nebula.
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These are the Pillars
of Creation.
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And this is
the Horsehead nebula,
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an enormous star nursery.
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What scientists have been
trying to figure out
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is what triggers
the star-making process.
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One possibility is that
a nearby supernova explosion
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took place...
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...and rammed into
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this otherwise innocuous
molecular cloud...
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...smushing it, smashing it,
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compressing it down so that
gravity could take over.
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Narrator:
Once gravity takes over,
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the cloud begins to shrink,
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sucking in more and more gas
into a giant, spinning disk.
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Gravity at the center
crushes everything
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into a dense, superhot ball...
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...that gets hotter and hotter.
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Suddenly,
atoms in the gas begin to fuse,
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and the star ignites.
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The leftover dust and debris
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forms a disk spinning around
the new star.
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It contains the seeds
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of planets, moons, comets,
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and asteroids.
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In 2001,
the Hubble space telescope
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was scanning the Orion nebula
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and took this image
of a young star
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surrounded by
one of these disks.
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It's a picture of
a solar system being born.
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Whenever I look at these
beautiful pictures of nebulae,
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the thing that really gets me
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is that these are baby pictures
of our own solar system.
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We looked like that once.
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Narrator: These fuzzy images
have opened the door
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to understanding
how planetary systems form.
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We have this
marvelous first-ever tool
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by which we can take pictures
of planets
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caught in the act of formation.
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It's quite
a marvelous opportunity
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for us to see the planets
around other stars forming,
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thereby giving us a glimpse
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as to how our own solar system
must surely have formed.
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Narrator: Scientists understood
where stars come from
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but not how planets grow
from the disk of gas and dust.
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The answer was discovered
by accident
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aboard the International
Space Station.
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Astronaut Don Pettit
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was experimenting with grains
of sugar and salt
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in the weightlessness of space.
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Stanley Love was watching
from Mission Control
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when Pettit stumbled
onto the process
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of how planets form
from cosmic dust.
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Well, one of Don's
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Saturday-morning
science projects
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was to take the bags
that we store drinks in
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and he put other stuff in it,
like salt and sugar,
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and there was one bag that he
just left the coffee powder in.
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Then he inflated the bags,
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and with these particles
in them,
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noticed that the particles would
just clump up immediately.
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They make a little dust bunny.
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Man: We'll be spending
some time watching that.
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I said,
"Don, this is incredible!
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You've just solved a 40-year-old
problem in planetary science!"
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Narrator: Astronaut Pettit
had discovered something big.
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In the zero gravity of space,
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particles of dust
don't float apart,
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they clump together.
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This is how mighty planets
are made from cosmic dust.
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The dust particles would collide
and stick and grow
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into ever larger dust particles
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and eventually rocks
and eventually boulders.
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Narrator:
The bigger the boulder,
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the more gravity it has.
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It begins to eat up everything
around it and grows bigger.
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It becomes larger, heavier,
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and consumes bigger
and bigger rocks.
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Eventually, some of these rocks
grow into planets.
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This is what happened
in our solar system
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4.6 billion years ago.
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There were
about 100 young planets
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all orbiting the new Sun.
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Collisions were inevitable.
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Narrator: At the beginning,
solar systems are violent.
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Ours was no different.
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It began with about
100 small, new planets.
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So, how did it go
from 100 small planets
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to the 8 major planets of today?
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We got the answer
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by studying the evolution
of other solar systems.
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We see solar systems
forming planets,
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and all of a sudden, they had
these giant disks around them.
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Those disks must be
from huge collisions.
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Narrator: If planets are smashing
together in other systems,
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they probably smashed together
in our own.
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We now know that
all solar systems do this
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before they settle down.
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It's the way they're built.
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The nice, neat, orderly
solar system that we see today
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has not always been the case.
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In the early days -- a few
million years, basically,
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after the planets
started forming --
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there were dozens, maybe even
hundreds of these young planets
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that were bouncing around
the solar system.
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They would smash
into each other.
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Sometimes they would collect
and get to be bigger planets.
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Sometimes they would smash
each other
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and turn into little bits.
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Narrator: There was heavy traffic
in the new solar system,
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objects of all sizes.
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They were bound to collide.
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Some of the planets
grew larger,
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and so did the collisions.
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I like to try to imagine
what it would have been like
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to actually stand
on the early Earth
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and look up into the night sky.
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Things would have looked
different.
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Narrator:
Planet hit planet.
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Only the largest survive.
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The rest are smashed to pieces.
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Something very large struck
the young planet Mercury.
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It blew the crust off
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and left behind
just the iron core.
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And the young planet Earth
did not escape, either.
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Dr. Plait:
A planet-sized object
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slammed into the Earth
off-center
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and blew a huge amount of
the Earth's crust into space.
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The debris circled
around the Earth...
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And eventually coalesced
to become the moon.
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Narrator: This demolition derby
raged for 500 million years.
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Dr. Plait:
What we see now --
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Mars and Earth and Mercury
and Venus --
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these planets
in the inner solar system --
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they're the survivors.
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They're the ones who lived
through these giant impacts.
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Narrator: Debris
from smashed infant planets
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ended up in the Asteroid Belt --
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a junkyard of rocky,
leftover planet parts.
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Most of the big impacts
happened
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in the inner solar system.
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But one of
the outer planets, Uranus,
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was also hit
and knocked on its side.
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A mystery, since the outer
planets formed mostly from gas
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and largely escaped the violence
of the inner solar system.
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These rocky cores formed.
The gas accumulated around them.
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This process actually happened
very rapidly,
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in astronomical terms,
in only about a million years.
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And those are the giant planets
we see today.
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Narrator: Beyond the gas giants,
Jupiter and Saturn,
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are Uranus and Neptune.
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These two are made
of gas and ice.
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And beyond them
lies the Kuiper Belt,
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a band of orbiting icy rocks
and dwarf planets.
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We used to think that one
Kuiper Belt object, Pluto,
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was the ninth planet.
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We've since decided that Pluto
is, in fact, a dwarf planet --
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one of many orbiting
more than 3 billion miles
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from the Sun.
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There are millions
of these things out there.
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They're so far away and so faint
that they're hard to see.
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These are leftover
from the formation
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of the solar system itself.
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Narrator: The Kuiper Belt marks
the edge of the Sun's influence.
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There is no warmth
and not much light
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way out here.
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But the Kuiper Belt is not
the end of our solar system.
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A shell of trillions
of icy objects,
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called the Oort Cloud,
is even further out.
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The Oort Cloud is so far away,
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light from the Sun
takes a full year to reach it.
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From the cold outer edge
to the hot star at the center,
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our solar system seems stable.
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Everything appears orderly
and in its proper place.
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But something isn't right.
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Uranus and Neptune
are in the wrong place.
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Narrator:
The planets of the solar system
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00:17:42,595 --> 00:17:46,190
grew from a giant disk
of dust and gas --
253
00:17:46,199 --> 00:17:51,035
the four inner rocky planets
close to the Sun,
254
00:17:51,037 --> 00:17:54,234
and the giant gas planets
farther out.
255
00:17:56,609 --> 00:17:59,977
But Uranus and Neptune
seem out of place.
256
00:18:04,517 --> 00:18:07,509
There wasn't enough stuff
this far from the Sun
257
00:18:07,520 --> 00:18:10,148
to make such big planets.
258
00:18:10,156 --> 00:18:13,683
So, what are they doing
out here?
259
00:18:13,693 --> 00:18:17,095
That led us to a theory
where Uranus and Neptune
260
00:18:17,096 --> 00:18:19,064
formed very close to the Sun
261
00:18:19,065 --> 00:18:22,091
and were actually
violently pushed outward.
262
00:18:26,105 --> 00:18:29,234
Narrator: So, what could shove
two massive planets
263
00:18:29,242 --> 00:18:31,108
clear across the solar system?
264
00:18:31,110 --> 00:18:33,010
We believe
that Jupiter and Saturn
265
00:18:33,012 --> 00:18:34,844
got into this funny
configuration
266
00:18:34,847 --> 00:18:38,283
where Jupiter went around
the Sun exactly twice
267
00:18:38,284 --> 00:18:41,879
every time
Saturn went around once.
268
00:18:41,888 --> 00:18:44,482
And that configuration
269
00:18:44,490 --> 00:18:47,084
allows the planets
to kick each other more
270
00:18:47,093 --> 00:18:48,618
as they pass one another,
271
00:18:48,628 --> 00:18:51,256
and that caused the
whole system to go nuts.
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Narrator: The combined gravity
of Jupiter and Saturn
273
00:18:58,271 --> 00:19:00,569
yanked hard on Uranus
and Neptune
274
00:19:00,573 --> 00:19:04,544
and pulled them
away from the Sun.
275
00:19:04,544 --> 00:19:06,103
As they moved outward,
276
00:19:06,112 --> 00:19:09,946
the two planets plowed through
asteroids and other debris
277
00:19:09,949 --> 00:19:13,385
leftover from the formation
of the other planets.
278
00:19:13,386 --> 00:19:15,480
[crashing]
279
00:19:27,000 --> 00:19:31,164
This sent billions of chunks of
rock flying in all directions.
280
00:19:38,578 --> 00:19:42,242
Some rocks
formed the Asteroid Belt.
281
00:19:42,248 --> 00:19:47,709
But most were thrown out
to create the vast Kuiper Belt.
282
00:19:51,858 --> 00:19:54,520
Dr. Levison: The analogy I like to
use is, think of a bowling match.
283
00:19:54,527 --> 00:19:57,895
And the bowling balls go down,
and the pins just go kaplooey.
284
00:19:57,897 --> 00:19:59,991
That's what happened in the
outer part of the solar system.
285
00:20:03,136 --> 00:20:05,264
Narrator:
The gravitational push
286
00:20:05,271 --> 00:20:07,740
from Jupiter and Saturn
was so strong,
287
00:20:07,740 --> 00:20:10,971
it may have reversed
the position of the two planets.
288
00:20:10,977 --> 00:20:14,140
It looks like it's possible
that Uranus and Neptune
289
00:20:14,147 --> 00:20:16,639
actually formed
in the opposite order.
290
00:20:16,649 --> 00:20:19,243
Neptune was closer
to the Sun than Uranus,
291
00:20:19,252 --> 00:20:21,550
but these gravitational
interactions
292
00:20:21,554 --> 00:20:23,613
actually swapped
their positions.
293
00:20:27,994 --> 00:20:30,053
Narrator:
It was the blizzard of rocks
294
00:20:30,063 --> 00:20:31,690
that Uranus and Neptune
ran into
295
00:20:31,698 --> 00:20:33,598
that acted like a brake
296
00:20:33,599 --> 00:20:37,365
and slowed them into the orbits
they keep today.
297
00:20:39,305 --> 00:20:43,003
The idea of planets changing
orbits may sound crazy,
298
00:20:43,009 --> 00:20:47,037
but scientists have seen it
happen in other solar systems.
299
00:20:47,046 --> 00:20:52,780
So now they think it's just
the way all solar systems work.
300
00:20:52,785 --> 00:20:55,345
When we look out into the galaxy
301
00:20:55,354 --> 00:20:58,688
and look at planets
around other stars,
302
00:20:58,691 --> 00:21:00,022
we see lots of evidence
303
00:21:00,026 --> 00:21:02,654
of those kind of events
happening elsewhere.
304
00:21:05,565 --> 00:21:07,033
Narrator:
In one far-off system,
305
00:21:07,033 --> 00:21:08,592
scientists have spotted
306
00:21:08,601 --> 00:21:11,263
something completely
off the charts --
307
00:21:11,270 --> 00:21:13,432
a planet as big as Jupiter,
308
00:21:13,439 --> 00:21:17,069
but it's not acting
like the Jupiter we know.
309
00:21:19,278 --> 00:21:21,076
Some of these giant planets
310
00:21:21,080 --> 00:21:24,311
are found orbiting very close
to their host star,
311
00:21:24,317 --> 00:21:26,684
taking only days --
a few days --
312
00:21:26,686 --> 00:21:28,711
to go around the host star.
313
00:21:31,290 --> 00:21:34,157
Obviously,
such close-in Jupiters
314
00:21:34,160 --> 00:21:36,424
are blowtorched by the star,
315
00:21:36,429 --> 00:21:39,091
raising the temperature
of the planet
316
00:21:39,098 --> 00:21:41,760
up to 1,000 or 2,000
degrees Celsius.
317
00:21:41,768 --> 00:21:46,638
Narrator: There's no way a gas giant
could have formed this close in.
318
00:21:46,639 --> 00:21:48,141
It's way too hot.
319
00:21:48,141 --> 00:21:52,510
The only explanation is that
it must have formed out there
320
00:21:52,512 --> 00:21:55,277
and then moved in here.
321
00:22:02,054 --> 00:22:04,352
The same thing
could have happened
322
00:22:04,357 --> 00:22:05,825
in our own solar system.
323
00:22:07,994 --> 00:22:11,862
Scientists have found large
amounts of the element lithium
324
00:22:11,864 --> 00:22:13,593
on the surface of the Sun.
325
00:22:17,403 --> 00:22:20,737
Lithium doesn't normally
exist in stars,
326
00:22:20,740 --> 00:22:23,107
but it is found in gas planets.
327
00:22:26,813 --> 00:22:29,441
Maybe there was
another gas giant
328
00:22:29,448 --> 00:22:31,177
in our own solar system
329
00:22:31,184 --> 00:22:34,381
that spiraled in
and crashed into the Sun.
330
00:22:34,387 --> 00:22:37,186
That would explain
how the lithium got there.
331
00:22:48,067 --> 00:22:49,831
Something very violent happened.
332
00:22:52,638 --> 00:22:55,198
Could it have been one
of these Jupiter-size planets
333
00:22:55,208 --> 00:22:57,370
getting thrown in
toward the Sun long ago?
334
00:22:57,376 --> 00:23:00,209
Narrator:
In the beginning,
335
00:23:00,213 --> 00:23:03,581
solar systems
are violent and messy,
336
00:23:03,583 --> 00:23:08,384
but, over time, they settle down
and become more stable.
337
00:23:08,387 --> 00:23:11,220
But stability is an illusion.
338
00:23:11,224 --> 00:23:13,420
Any planet in the solar system
339
00:23:13,426 --> 00:23:17,920
is always in danger
of total annihilation.
340
00:23:23,302 --> 00:23:25,168
Narrator: There are all kinds
of solar systems
341
00:23:25,171 --> 00:23:27,003
in the Milky Way galaxy.
342
00:23:27,006 --> 00:23:30,567
Most seem strange
compared to our own.
343
00:23:30,576 --> 00:23:33,807
Some planets
follow crazy orbits.
344
00:23:33,813 --> 00:23:37,078
Some smash into each other.
345
00:23:42,955 --> 00:23:46,152
Others dive into their stars.
346
00:23:53,866 --> 00:23:57,734
So, why are the orbits
of our own planets
347
00:23:57,737 --> 00:23:59,831
so regular and stable?
348
00:23:59,839 --> 00:24:03,173
Well, that's because all the
planets have motion left over
349
00:24:03,175 --> 00:24:05,576
from the formation
of the solar system.
350
00:24:05,578 --> 00:24:08,343
When the nebula collapsed
around the Sun,
351
00:24:08,347 --> 00:24:11,840
as the Sun was forming,
there was an intrinsic motion,
352
00:24:11,851 --> 00:24:14,343
and that gave our planet
a velocity.
353
00:24:14,353 --> 00:24:18,187
Literally, we are falling freely
toward the Sun at all times,
354
00:24:18,190 --> 00:24:21,057
but we're going so fast,
we keep missing it.
355
00:24:21,060 --> 00:24:22,653
That's what an orbit is.
356
00:24:22,662 --> 00:24:26,496
[riders screaming]
357
00:24:26,499 --> 00:24:28,729
Narrator:
Think of a merry-go-round.
358
00:24:28,734 --> 00:24:30,099
The faster it spins,
359
00:24:30,102 --> 00:24:33,367
the farther and farther
you're thrown from the center.
360
00:24:33,372 --> 00:24:35,739
When it slows down,
361
00:24:35,741 --> 00:24:39,644
you lose momentum
and fall back inwards.
362
00:24:42,014 --> 00:24:44,881
It's something like that
with planets.
363
00:24:44,884 --> 00:24:49,651
The disk that gave birth
to the planets was spinning,
364
00:24:49,655 --> 00:24:52,147
and the momentum
leftover from that
365
00:24:52,158 --> 00:24:54,957
keeps everything going around
to this day.
366
00:24:57,430 --> 00:25:00,161
Moving at 66,000 miles an hour,
367
00:25:00,166 --> 00:25:03,192
the Earth takes one year
to orbit the Sun.
368
00:25:03,202 --> 00:25:06,502
Planets farther from the Sun
have bigger orbits,
369
00:25:06,505 --> 00:25:09,770
move slower, and take longer.
370
00:25:09,775 --> 00:25:14,076
Saturn orbits the Sun
once every 29 years.
371
00:25:16,816 --> 00:25:21,720
Neptune takes 164 years.
372
00:25:21,721 --> 00:25:26,056
Each planet stays on
a precise path around the Sun,
373
00:25:26,058 --> 00:25:28,686
and for us, that's a good thing.
374
00:25:30,696 --> 00:25:34,394
Marcy: Our solar system
has a somewhat fortunate
375
00:25:34,400 --> 00:25:36,198
spacing of the planets,
376
00:25:36,202 --> 00:25:38,466
with nearly circular orbits,
377
00:25:38,471 --> 00:25:41,566
which keeps
the whole house of cards
378
00:25:41,574 --> 00:25:45,101
from falling apart, crumbling,
scattering to the wind.
379
00:25:50,983 --> 00:25:53,213
If our solar system did not have
380
00:25:53,219 --> 00:25:56,314
nice, neat, stable,
nearly circular orbits,
381
00:25:56,322 --> 00:25:57,847
the Earth wouldn't be here
382
00:25:57,857 --> 00:26:00,155
and we wouldn't be here
talking about it.
383
00:26:05,031 --> 00:26:08,160
Narrator: The planets
are on safe, stable orbits...
384
00:26:10,736 --> 00:26:13,865
...but billions of comets
and asteroids are not.
385
00:26:18,344 --> 00:26:22,872
Many come streaking
into the inner solar system.
386
00:26:22,882 --> 00:26:25,943
And when they do, watch out.
387
00:26:34,527 --> 00:26:38,327
Dr. Levison: The meteor crater
which we see here today
388
00:26:38,330 --> 00:26:42,358
formed as a result of
a 150-foot rocky iron object
389
00:26:42,368 --> 00:26:45,497
coming in
and slamming into the Earth
390
00:26:45,504 --> 00:26:47,563
roughly 50,000 years ago.
391
00:26:47,573 --> 00:26:53,012
Narrator: Some of the objects
coming our way can be much bigger.
392
00:26:53,012 --> 00:26:54,878
Look at the moon.
393
00:26:54,880 --> 00:26:58,942
It's covered
with large impact craters.
394
00:26:58,951 --> 00:27:02,251
Earth has been hit, too --
a lot.
395
00:27:07,860 --> 00:27:09,851
But the craters have eroded.
396
00:27:11,530 --> 00:27:15,398
We know that a huge asteroid
smashed into the Earth,
397
00:27:15,401 --> 00:27:18,894
off the coast of Mexico,
65 million years ago.
398
00:27:18,904 --> 00:27:22,704
It was going
45,000 miles an hour,
399
00:27:22,708 --> 00:27:24,506
and when it hit,
400
00:27:24,510 --> 00:27:28,276
it released more energy
than 5 billion Hiroshima bombs.
401
00:28:02,548 --> 00:28:06,485
It wiped out 70% of life
on Earth.
402
00:28:12,958 --> 00:28:17,589
A few more impacts like that
could destroy all life on Earth.
403
00:28:17,596 --> 00:28:22,033
But, believe it or not,
Earth has a giant bodyguard.
404
00:28:24,570 --> 00:28:26,800
Jupiter is more
than just another pretty face
405
00:28:26,805 --> 00:28:28,068
through the telescope.
406
00:28:28,073 --> 00:28:30,337
It's actually really important
for life on Earth.
407
00:28:30,342 --> 00:28:31,901
Jupiter's gravity is so huge
408
00:28:31,911 --> 00:28:34,869
and it's just in the right place
in the solar system,
409
00:28:34,880 --> 00:28:37,144
that it protects the Earth
from comets
410
00:28:37,149 --> 00:28:39,447
that come from deep
in the solar system
411
00:28:39,451 --> 00:28:44,082
and swing by the Sun and could
possibly hit the Earth.
412
00:28:44,089 --> 00:28:46,387
Dr. Levison:
Jupiter plays the role
413
00:28:46,392 --> 00:28:49,384
of the biggest baseball bat
in the solar system.
414
00:28:49,395 --> 00:28:50,863
As these comets come by,
415
00:28:50,863 --> 00:28:54,299
most of them get knocked out
of the solar system by Jupiter.
416
00:28:57,303 --> 00:28:58,862
Narrator: In 1994,
417
00:28:58,871 --> 00:29:03,468
comet Shoemaker-Levy 9 raced
toward the inner solar system.
418
00:29:06,178 --> 00:29:08,647
But it never got past Jupiter.
419
00:29:11,350 --> 00:29:14,843
Astronomers watched
as Jupiter tore it to pieces
420
00:29:14,853 --> 00:29:18,585
and dragged its remains
down to the planet's surface.
421
00:29:21,594 --> 00:29:23,551
We have seen comets
smash into Jupiter,
422
00:29:23,562 --> 00:29:25,929
creating fireballs that were
bigger than the Earth.
423
00:29:31,804 --> 00:29:34,501
Narrator: They were
the biggest explosions
424
00:29:34,506 --> 00:29:36,304
ever seen in our solar system.
425
00:29:39,878 --> 00:29:42,370
Dr. Thaller:
Had that comet hit us,
426
00:29:42,381 --> 00:29:43,940
it would have resurfaced
the planet.
427
00:29:43,949 --> 00:29:45,849
It would have been the end
of life as we know it.
428
00:29:45,851 --> 00:29:47,046
Dr. Levison:
If Jupiter wasn't there,
429
00:29:47,052 --> 00:29:49,419
we believe that the impact rate
on the Earth
430
00:29:49,421 --> 00:29:53,255
would be something like 1,000
times more than we see today.
431
00:30:01,166 --> 00:30:04,659
Narrator: Lucky for us,
Earth has the perfect orbit.
432
00:30:06,272 --> 00:30:09,765
Jupiter protects us
from asteroids and comets.
433
00:30:12,645 --> 00:30:15,376
We're close enough to the Sun
for liquid water
434
00:30:15,381 --> 00:30:18,476
but not so close
that it boils away.
435
00:30:18,484 --> 00:30:23,285
It's just the right combination
for life.
436
00:30:25,724 --> 00:30:27,055
Question is,
437
00:30:27,059 --> 00:30:29,960
if our solar system could create
the perfect conditions,
438
00:30:29,962 --> 00:30:32,260
could other solar systems
do it, too?
439
00:30:33,932 --> 00:30:37,095
Planet hunters have spotted
a solar system
440
00:30:37,102 --> 00:30:38,661
20 light-years away,
441
00:30:38,671 --> 00:30:41,663
and it has a planet
just the right size
442
00:30:41,674 --> 00:30:43,631
in just the right place.
443
00:30:49,315 --> 00:30:52,580
Narrator: Astronomers around the
world are looking for new planets
444
00:30:52,584 --> 00:30:55,417
in distant solar systems.
445
00:30:57,523 --> 00:31:01,391
So far, they've discovered
more than 420.
446
00:31:07,433 --> 00:31:10,425
Most are huge gas giants,
like Jupiter...
447
00:31:14,606 --> 00:31:17,576
...but they're either very close
to the star
448
00:31:17,576 --> 00:31:19,544
or much farther away.
449
00:31:27,619 --> 00:31:32,284
Then, in 2005, astronomers
made an exciting discovery.
450
00:31:35,794 --> 00:31:40,425
They detected a solar system
with rocky planets like our own.
451
00:31:43,402 --> 00:31:49,171
These planets orbit a star
called Gliese 581.
452
00:31:49,174 --> 00:31:52,667
This star, Gliese 581,
and its 4 planets
453
00:31:52,678 --> 00:31:56,512
is, frankly, quite bizarre
relative to our solar system.
454
00:31:56,515 --> 00:31:59,746
The four planets we know of
455
00:31:59,752 --> 00:32:02,483
all orbit very close
to the host star,
456
00:32:02,488 --> 00:32:04,650
all four of them orbiting closer
457
00:32:04,656 --> 00:32:07,717
than the planet Mercury,
our closest planet,
458
00:32:07,726 --> 00:32:08,818
orbits the Sun.
459
00:32:13,665 --> 00:32:16,566
Narrator:
But Gliese 581 is a small star.
460
00:32:16,568 --> 00:32:18,434
It doesn't burn as brightly
461
00:32:18,437 --> 00:32:21,065
or give off as much heat
as our Sun,
462
00:32:21,073 --> 00:32:24,441
so the planets can orbit
much closer
463
00:32:24,443 --> 00:32:26,605
without being vaporized.
464
00:32:26,612 --> 00:32:30,810
Dr. Thaller: We know of four
planets going around this star,
465
00:32:30,816 --> 00:32:33,615
and a few of them
are quite interesting.
466
00:32:33,619 --> 00:32:36,953
There's one that's only
about twice the mass of Earth.
467
00:32:36,955 --> 00:32:39,788
Now, that particular one
is very close to the star.
468
00:32:39,792 --> 00:32:42,227
It's probably very hot --
too hot for life.
469
00:32:42,227 --> 00:32:43,490
But there's another one,
470
00:32:43,495 --> 00:32:45,657
about eight times the mass
of the Earth,
471
00:32:45,664 --> 00:32:48,099
which is getting far enough away
from the star
472
00:32:48,100 --> 00:32:50,194
that it might be
in the habitable zone.
473
00:32:50,202 --> 00:32:52,330
Narrator: Like Earth,
474
00:32:52,337 --> 00:32:56,205
this planet orbits at a distance
where water is a liquid.
475
00:32:58,977 --> 00:33:03,778
And where there's liquid water,
there could be oceans and life.
476
00:33:18,764 --> 00:33:23,224
In March 2009, NASA launched
the Kepler Space Telescope.
477
00:33:23,235 --> 00:33:24,532
Its mission --
478
00:33:24,536 --> 00:33:27,836
to search for planets
similar to our own
479
00:33:27,840 --> 00:33:30,366
in new solar systems.
480
00:33:32,678 --> 00:33:35,670
Marcy: We may find planets that
have methane atmospheres...
481
00:33:41,687 --> 00:33:44,054
...that have
ammonia atmospheres.
482
00:33:47,893 --> 00:33:51,454
We may find planets that are
covered in heavy organics...
483
00:33:53,332 --> 00:33:55,630
...a tarlike material.
484
00:33:58,737 --> 00:34:01,502
We may find some
that are covered by water.
485
00:34:04,409 --> 00:34:06,673
I think one of
the glorious quests here
486
00:34:06,678 --> 00:34:08,976
in the next decade or two
487
00:34:08,981 --> 00:34:11,848
is to learn
the full diversity
488
00:34:11,850 --> 00:34:13,818
of the family
of Earth-like planets
489
00:34:13,819 --> 00:34:15,810
that may be out there
in the universe.
490
00:34:20,225 --> 00:34:21,693
Narrator: With Kepler,
491
00:34:21,693 --> 00:34:24,390
astronomers expect
to discover hundreds,
492
00:34:24,396 --> 00:34:27,058
possibly thousands,
of new solar systems.
493
00:34:31,203 --> 00:34:34,161
Dr. Thaller: Think about
our own Milky Way galaxy.
494
00:34:34,172 --> 00:34:38,734
The galaxy has roughly
500 billion to a trillion stars.
495
00:34:38,744 --> 00:34:43,705
Some fairly large percentage
of that have planets.
496
00:34:43,715 --> 00:34:46,707
Now, think about how many
galaxies we know of.
497
00:34:46,718 --> 00:34:49,688
We certainly haven't found
all the galaxies
498
00:34:49,688 --> 00:34:51,087
in the universe yet.
499
00:34:51,089 --> 00:34:53,717
But the ones
we can take a picture of
500
00:34:53,725 --> 00:34:56,387
are actually
about 60 billion galaxies.
501
00:34:59,965 --> 00:35:03,162
When you look up
at the night sky tonight,
502
00:35:03,168 --> 00:35:05,796
simply in the path
of your sight,
503
00:35:05,804 --> 00:35:09,331
even if you can't see it,
504
00:35:09,341 --> 00:35:14,108
there are billions of
solar systems all around you.
505
00:35:14,112 --> 00:35:17,082
Narrator: And there could be
a solar system
506
00:35:17,082 --> 00:35:19,915
with a planet just like Earth.
507
00:35:21,954 --> 00:35:25,788
If it happened once,
it could happen again.
508
00:35:31,630 --> 00:35:35,191
Solar systems
don't last forever.
509
00:35:35,200 --> 00:35:37,168
Orbits fall apart.
510
00:35:37,169 --> 00:35:38,830
Planets collide.
511
00:35:38,837 --> 00:35:40,965
It might happen to us.
512
00:35:40,973 --> 00:35:43,203
But even if it doesn't,
513
00:35:43,208 --> 00:35:45,734
in another 5 billion years,
514
00:35:45,744 --> 00:35:50,306
a catastrophe will end
our solar system as we know it.
515
00:35:59,091 --> 00:36:03,153
Narrator: Nothing lasts forever,
not even solar systems.
516
00:36:03,161 --> 00:36:05,323
Ours may seem stable now,
517
00:36:05,330 --> 00:36:09,233
but, actually,
it's very slowly coming apart.
518
00:36:15,007 --> 00:36:18,033
Dr. Plait: If the solar system
was chaotic in the past,
519
00:36:18,043 --> 00:36:20,569
that doesn't mean
it's all settled down now.
520
00:36:20,579 --> 00:36:22,411
There is still a possibility
521
00:36:22,414 --> 00:36:25,076
of a little bit of chaos
in the future.
522
00:36:25,083 --> 00:36:26,778
Narrator: In the future,
523
00:36:26,785 --> 00:36:30,312
the gravitational pull
of the planets on each other
524
00:36:30,322 --> 00:36:32,950
will gradually disrupt
their orbits.
525
00:36:32,958 --> 00:36:36,519
Perhaps,
over the billions of years,
526
00:36:36,528 --> 00:36:40,294
the planets will jostle each
other in this gravitational way
527
00:36:40,298 --> 00:36:41,697
so that, eventually,
528
00:36:41,700 --> 00:36:44,795
two of the planets
will come close to each other.
529
00:36:48,807 --> 00:36:51,777
When that happens --
and it will --
530
00:36:51,777 --> 00:36:56,180
those two planets will engage
in a sort of a do-si-do,
531
00:36:56,181 --> 00:36:59,811
flinging one or the other
of them, maybe both,
532
00:36:59,818 --> 00:37:01,286
into wild orbits,
533
00:37:01,286 --> 00:37:05,280
perhaps ejecting one or both
of them from the solar system.
534
00:37:07,693 --> 00:37:10,993
Narrator: Mars could be thrown
out of the solar system,
535
00:37:10,996 --> 00:37:13,431
and Mercury might crash
into the Earth.
536
00:37:25,310 --> 00:37:29,008
The entire house of cards
that is our solar system
537
00:37:29,014 --> 00:37:31,073
would completely fall apart.
538
00:37:31,083 --> 00:37:35,213
Narrator:
Solar systems begin and end
539
00:37:35,220 --> 00:37:38,747
with a lot of collisions
and destruction.
540
00:37:38,757 --> 00:37:40,555
But don't panic yet.
541
00:37:42,327 --> 00:37:44,762
Dr. Plait: This is gonna take
billions of years,
542
00:37:44,763 --> 00:37:46,959
but over the lifetime
of the solar system,
543
00:37:46,965 --> 00:37:49,593
these are eventualities
that could come to pass.
544
00:37:49,601 --> 00:37:53,435
Narrator:
But one way or another,
545
00:37:53,438 --> 00:37:56,567
our solar system is doomed.
546
00:37:59,444 --> 00:38:02,175
Like all solar systems,
the end will come
547
00:38:02,180 --> 00:38:06,174
when the star
at the center dies.
548
00:38:06,184 --> 00:38:09,643
In 5 billion years,
549
00:38:09,654 --> 00:38:12,646
our own star
will run out of fuel
550
00:38:12,657 --> 00:38:15,149
and become a red giant.
551
00:38:17,395 --> 00:38:21,696
It'll heat up, swell,
and engulf the inner planets.
552
00:38:27,873 --> 00:38:31,002
The Earth's surface
will be scorched...
553
00:38:34,346 --> 00:38:37,782
...the seas will evaporate...
554
00:38:37,783 --> 00:38:40,582
And the land will melt.
555
00:38:46,024 --> 00:38:50,052
Dr. Thaller: The Sun will become about
as big as where the Earth's orbit is,
556
00:38:50,061 --> 00:38:52,496
so a likely scenario for the end
of the world
557
00:38:52,497 --> 00:38:55,228
is that we're going to be inside
the Sun for a while.
558
00:39:07,479 --> 00:39:10,881
Dr. Plait: The Earth's gonna get
swallowed right up into the Sun,
559
00:39:10,882 --> 00:39:13,249
and it's gonna be toast --
vapor, literally.
560
00:39:14,886 --> 00:39:16,479
Narrator:
After a while,
561
00:39:16,488 --> 00:39:18,786
the red giant
will fall apart, too,
562
00:39:18,790 --> 00:39:23,751
leaving behind a tiny corpse
of a star called a white dwarf.
563
00:39:34,472 --> 00:39:36,907
Dr. Thaller: It'll be
about the size of the Earth,
564
00:39:36,908 --> 00:39:39,707
and it will cool off over many
millions or billions of years.
565
00:39:44,516 --> 00:39:47,417
That will be the real end
of our solar system.
566
00:39:53,491 --> 00:39:55,152
Marcy: From the Earth --
567
00:39:55,160 --> 00:39:58,186
this dead, rocky planet
that used to harbor
568
00:39:58,196 --> 00:40:00,858
an enormously vibrant
civilization --
569
00:40:00,866 --> 00:40:03,927
we will look out...
570
00:40:03,935 --> 00:40:08,133
And there will be this fairly
faint dot which is our Sun,
571
00:40:08,139 --> 00:40:12,167
now a white dwarf,
a dying, almost dead star.
572
00:40:15,680 --> 00:40:17,774
Narrator: The remains
of the inner planets
573
00:40:17,782 --> 00:40:19,716
will continue to orbit
the white dwarf.
574
00:40:25,957 --> 00:40:30,224
But the giant outer planets
will live on, untouched.
575
00:40:33,765 --> 00:40:35,460
Marcy:
They will have warmed up
576
00:40:35,467 --> 00:40:37,458
during the red-giant phase
of the Sun.
577
00:40:37,469 --> 00:40:40,302
But once the Sun
is a white dwarf,
578
00:40:40,305 --> 00:40:43,935
those giant planets
will survive just as well,
579
00:40:43,942 --> 00:40:46,604
holding on to their hydrogen
and helium,
580
00:40:46,611 --> 00:40:48,978
albeit colder
than they used to be,
581
00:40:48,980 --> 00:40:52,280
because that white dwarf will
no longer be warming them up.
582
00:40:58,757 --> 00:41:02,284
Narrator: Even though this is
5 billion years in the future
583
00:41:02,294 --> 00:41:03,625
for our solar system,
584
00:41:03,628 --> 00:41:05,289
it may already have happened
585
00:41:05,297 --> 00:41:08,028
to many other systems
throughout the universe.
586
00:41:11,836 --> 00:41:15,306
Our solar system
emerged from chaos
587
00:41:15,307 --> 00:41:17,366
to eventually support life.
588
00:41:17,375 --> 00:41:18,638
We were lucky.
589
00:41:18,643 --> 00:41:21,806
We've just the right amount
of planets,
590
00:41:21,813 --> 00:41:23,110
in the right place,
591
00:41:23,114 --> 00:41:25,674
at the right distance
from each other,
592
00:41:25,684 --> 00:41:28,153
all orbiting
the right type of star.
593
00:41:28,153 --> 00:41:33,182
But it could have been
a very different story.
594
00:41:33,191 --> 00:41:35,023
Dr. Thaller:
There are so many things
595
00:41:35,026 --> 00:41:37,051
that are fortunate
about our solar system,
596
00:41:37,062 --> 00:41:38,120
starting with the Sun.
597
00:41:38,129 --> 00:41:41,121
The Sun is a very stable,
easy star --
598
00:41:41,132 --> 00:41:44,397
a perfect thing
for life to evolve around.
599
00:41:44,402 --> 00:41:46,336
That's probably not
a coincidence that we're here.
600
00:41:48,340 --> 00:41:50,775
Narrator: An extraordinary
chain of events
601
00:41:50,775 --> 00:41:52,300
over billions of years
602
00:41:52,310 --> 00:41:55,336
have made our solar system
the perfect place
603
00:41:55,347 --> 00:41:57,679
for life to evolve.
604
00:42:04,022 --> 00:42:07,720
Dr. Plait: What we see today is not
the way things have always been
605
00:42:07,726 --> 00:42:09,922
and not the way things
will always be.
606
00:42:09,928 --> 00:42:11,054
We're not unique,
607
00:42:11,062 --> 00:42:13,190
but it is just the way
things worked out.
608
00:42:16,067 --> 00:42:18,331
Dr. Levison: The Earth has to be
in the right place.
609
00:42:18,336 --> 00:42:20,202
The planets had to be
in the right place.
610
00:42:20,205 --> 00:42:23,163
The giant planets have to be
in the right place
611
00:42:23,174 --> 00:42:25,506
to protect us from impacts.
612
00:42:28,079 --> 00:42:31,811
All that has to be right
in order to get life on Earth.
613
00:42:35,520 --> 00:42:38,785
Narrator: Ours is the only
planetary system we know
614
00:42:38,790 --> 00:42:40,087
that supports life.
615
00:42:40,091 --> 00:42:41,855
As solar systems go,
616
00:42:41,860 --> 00:42:46,161
does that make us extraordinary
or perfectly normal?
617
00:42:46,164 --> 00:42:48,292
We don't know.
618
00:42:48,299 --> 00:42:49,596
But every week,
619
00:42:49,601 --> 00:42:52,468
we're discovering
new solar systems
620
00:42:52,470 --> 00:42:53,904
with new planets.
621
00:42:53,905 --> 00:42:56,567
It could be
just a matter of time
622
00:42:56,574 --> 00:42:58,201
before we discover...
623
00:42:58,209 --> 00:43:00,371
We're not alone.